Self-bonding magnet wire and method



Jan. 31, 1967 TOSHIO UMEWAKA ETAL SELF-BONDING MAGNET WIRE AND METHOD Filed Sept. 9, 1964 Fig.

SELF -BONDED DOUBLE -COATED WIRE COIL INSULATING ENAMEL UNDER C OA T BONDING POLYVI/VYL ACE TAL AND RE SIN OUTER COA T Fig. 3

WIRE

COAT WITH ENAMEL I AND BAKE TO FORM FULL Y BAKED UNDERCOAT COAT WITH P v ACETAL AND RES/IV TO FORM OUTER COAT UNDERBAKE OUTER COAT WIND INTO COIL OF ADJACENT TURNS DIP IN CHLOR/NA TED A LIPHA TIC HYDROCARBON SOL VENT TO CAUSE OU TER COAT TO SWELL HEAT TO CAUSE SWOLLEN OUTER COAT TO BOND ADJACENT TURNS v .SEL F BONDED 'DOUBL E- 004 r50 WIRE co/L Toshio Umeivaka Hiroshi Kachi Noriyoshi Okubo Minoru Hirano INVENTORS United States Patent SELF-BONDING MAGNET WIRE AND METHOD Toshio Umewaka, Yokohama, Hiroshi Kachi, Hiratsuka, and Noriyoshi Okubo and Minoru Hirano, Yokohama, Japan, assignors to The Furukawa Electric Company Limited, Tokyo, Japan, a corporation of Japan Filed Sept. 9, 1964, Ser. No. 395,272 Claims priority, application Japan, Feb. 9, 1961, 36/ 4,468 Claims. (Cl. 29-15557) This application is a continuation-in-part of application Serial No. 170,822, now abandoned.

The present invention relates to a self bonding magnet wire in which an enamel outer coat consisting essentially of polyvinyl acetal resin, to which is added a thermosetting resin, is baked to form an adhesive layer on an insulated wire having a baked base film next to the conductor, the said outer coat being baked to such an extent as to swell or blister when tested in accordance with NEMA Standard MW 5495, 542.

In the case of the conventional self-bonding magnet wire, an insulating material consisting essentially of polyvinyl butyra-l, to which is added a thermoplastic resin, is coated and baked on an ordinary insulated wire. This double-coated insulated wire, after being formed into a coil, is electrified or otherwise heated to melt its outer coat and thus make its wire turns adhere to one another in a hardened condition. Such conventional self bonding magnet wire, however, has a defect of deforming due to softening of its outer coat when used at a temperature of about 100 C., because the outer coat contains a thermoplastic resin.

The outer coat of the self-bonding magnet wire of the invention does not cause a sufficient adhesion of wire turns even when the wire formed in a coil is electrified or otherwise heated. But, when the coil is dipped in a specified solvent such as dichloroethane for a short time, the outer coat swells, and, when the coil is taken out and heated at a temperature higher than the boiling point of the solvent, its wire turns adhere firmly to one another as the solvent on them evaporates. The coil thus finished never softens even at 100 C. to 150 C.

The object of the invention is therefore to obtain a self-bonding magnet wire which, when formed into a coil, causes its turns to adhere to one another through the aforementioned simple treatment of dipping the coil in a solvent and, after taking it out, heating it at a temperature higher than the boiling point of the solvent (instead of the ordinary complicated method aiming at the adhesion of wire turns by heating them for a long time after immersion under vacuum), and which develops no softening of its adhesive layer even when used at high temperature.

As stated above, the self-bonding magnet wire under the invention has a double-coating structure. We shall first describe the outer coat.

The enamel used for the outer coat consists essentially of polyvinyl acetal resin, to which is added a thermosetting resin, their ratio being 10 to 100 parts by weight, preferably 20 to 60 parts by weight, of the latter as against 100 parts by weight of the former.

As the thermosetting resin to be added to the enamel, phenol resin, epoxy resin, melamine resin, silicone resin, xylene resin, furane resin, and polyurethane resin can be used alone or two or more in admixture.

None of the enamels which make use of the above resins are new in composition. In case any of these enamels is baked on an ordinary insulated wire with a basic film of polyester, polyurethane, or acrylic enamel, such double-coated wire, when formed into a coil, does not develop any satisfactory adhesion of its turns when heated either as it is or after being dipped in a solvent, so

long as such outer coat is baked under the same conditions as under conventional methods.

In producing the self-bonding magnet wire under the invention, using as an outer coat any enamel comprising essentially polyvinyl acetal resin, to which is added a thermosetting resin, it is essential to give the outer coat under-baking instead of the standard baking usually in practice.

Generally, the degree of baking the enamel film is very difficult to specify. In respect of the practical use pro erties of the film, the National Electrical Manufacturers Association, Pub. No. MW 5-1955, 542, Completeness of Cure (Toluol-Alcohol Test), specifies that the enamel on wire, when dipped for five minutes in a boiling solution composed of 30% toluol and 70% ethyl alcohol (by volume) and visually inspected after being taken out, shall not have any swell or blister.

The inventors have learned that the insulated wire, on which an enamel comprising the above-mentioned polyvinyl acetal resin and thermosetting resin is baked in such a degree as to swell when tested according to the NEMA Standard, develops a very finm adhesion of its wire turns when formed into a coil, dipped in a solvent of chlorinated aliphatic hydrocarbons, and, after being taken out, heated at a temperature of C. to C.

The inventors have applied the above discovery to the outer coat of the self-bonding magnet wire and obtained a magnet wire that can form a coil capable of use at high temperature which is impracticable for conventional coils. To carry out the under-baking, the above outer coat is baked in a furnace, 2 to 10 meters long, at baking temperature of 200 C. to 400 C. at such a wire travelling speed within a range of 5 to 30 meters per minute that it swells or blisters when tested in accordance with the National Electrical Manufacturers Association, Pub. No. MW 5-1955, 542, Completeness of Cure (Toluol-Alcohol Test). The travelling speed above referred to naturally varies according to the wire diameter.

FIGS. 1 and 2 of the drawing illustrate perspective and cross-sectional views of the self-bonded double coated wire. The drawing also illustrates the process by a flow diagram.

With regard, now, to the base film, inasmuch as it is indispensable that the self-bonding magnet wire under present application should be clipped in a solvent after it is coiled, the wire is naturally required to have a highly solvent-resistant film. The enamels fit for this purpose are polyester enamel having a principal ingredient of terephthalic acid, polyurethane enamel, acrylic enamel, epoxy enamel, and modified silicone enamel. Polyvinyl formal enamel and oleoresinous enamel are unsuitable for use.

Solvents for use for dipping are chlorinated aliphatic hy-' drocarbons containing l-4 carbon atoms such as dichloroethane, dichloroethylene, dichloropropane, trichloroethane, trichloroethylene, trichloropropane, trichlorobutane, tetrachloromethane, and tetrachloroethane.

The invention will be further explained in detail by examples, wherein the part is to represent the weight part.

EXAMPLE 1 vide a double-coated wire having an outer coat of 0.015 mm. thickness.

wire having an outer coat layer of 0.015 mm. thickness.

EXAMPLE 3 A polyester resin insulated wire (0.035 mm. thick insulation) having an external diameter of 1.07 mrn., Which is produced in a 3 meter long furnace at a baking temperature of 380 C. and a travelling speed of 6 m./min., is coated on its external surface with a varnish consisting of 11 parts of polyvinyl formal resin, 9 parts of epoxy resin, 40 parts of solvent naphtha and 40 parts of cresylic acid, and heated in the above furnace at 350 C. and at a travelling speed of 8 rn./rnin., to provide a wire having an outer coat of 0.015 mm. thickness.

EXAMPLE 4 In the same process according to Example 1, a varnish consisting of 5 parts of polyvinyl formal resin, 5 parts of silicone resin, 40 parts of solvent naphtha and 40 parts of cresylic acid is used for the outer coat of the polyester insulated wire to provide a double-coated wire.

EXAMPLE .5

Under the same condition as in Example 1, a varnish consisting of 12 parts of polyvinyl formal resin, 8 parts of polyurethane resin, 40 parts of solvent naphtha and 40 parts of cresylic acid is used for the outer coat of the polyester insulated Wire to provide a similar double-coated wire.

EXAMPLE 6 Under the same condition as in Example 1, a varnish consisting of 14 parts of polyvinyl formal resin, 6 parts of xylene resin, 40 parts of solvent naphtha and 40 parts of cresylic acid is used for the outer coat of the polyester insulated wire to provide a similar double-coated wire.

EXAMPLE 7 According to the same condition as in Example 1, a varnish consisting of 14 parts of polyvinyl formal resin, 6 parts of furane resin, 40 parts of solvent naphtha and 40 parts of cresylic acid is used for the outer coat of the polyester. insulated Wire to provide a similar double-coated wire.

EXAMPLE 8 On the outside of a finished epoxy resin insulated wire (0.035 mm. thick insulation) having an external diameter of 1.07 mm, which is produced in a 3 meter long furnace at a baking temperature of 370 C. and a travelling speed of 7 m./min., is coated with a varnish consisting of 14 parts of polyvinyl formal resin, 6 parts of resole type phenolic resin, 40 parts of solvent naphtha and 40 parts .of cresylic acid, said varnish being heated in the above furnace at 350 C. and at a travelling speed of 7 m./min., to provide a double-coated wire having an outer coat of 0.015 mm. thickness.

EXAMPLE 9 In the same conditions as in Example 8, the silicone resin wire is used instead of the epoxy resin insulated wire to obtain a double-coated wire.

EXAMPLE 10 In the Example 8, acrylic resin insulated wire is used instead of the epoxy resin insulated Wire to provide a similar double-coated wire.

EXAMPLE 11 In the same conditions as in Example 8, polyurethane resin insulated Wire baked at 360 C. is used instead of epoxy resin insulated wire baked at 370 C. to provide a double-coated wire.

EXAMPLE 12 A polyester resin insulated wire having an external diameter of 1.07 min, insulation layer of 0.035 mm. thick, which is produced in a 7 meter long furnace at a baking temperature of 380 C. and a travelling speed of 12 m./ min, is coated on its external surface with a varnish consisting of 15 parts of polyvinyl formal resin, 5 parts of resole type phenolic resin, 40 parts of solvent naphtha and 40 parts of cresylic acid, and heated in the above furnace at 350 C. and at a travelling speed of 16 m./min., to provide a double-coated wire having an outer coat of 0.015 mm. thickness.

EXAMPLE 13 A polyester resin insulated wire (0.035 mm. thick insulation) having an external diameter of 1.07 mm., which is produced in a 7 meter long furnace at a heating temperature of 380 C. and a travelling speed of 12 m./min., is coated on its external surface with a varnish consisting of 12 parts of polyvinyl formal resin, 8 parts of epoxy resin, 40 parts of solvent pahtha and 40 parts of cresylic acid, and heated in the above furnace at 350 C. and at a travelling speed of 17 ni./min., to provide a doublecoated Wire having an outer coat of 0.015 mm. thickness.

The properties of the insulated wires of Examples 1, 2, 3, 12 and 13 of the invention, and those of the conventional polyester resin insulated wire (conductor diameter of 1.0 mm.; finished external diameter of 1.1 mm.) are shown in Table 1 for comparison; and those of the insulated wire obtained by Example 8 and the conventional self-bonding wire in Table 2.

Table 1 Test item Insulated Wires of the invention Conventional E 1 insulated wire Wound to its own (he Good.

Heat resistance (after heated t Do.

wound [or 3 times dirt).

Heat shock resistance (wound or a specified dia.. Twice dia., Twice dim, Twice dirt, 3 times dim,

heated to C. [or 1 ln'.). Good. Good. Good. Good.

Breakdown voltage, kv 13.8 13.5 .1 12.9 12.5.

Abrasion resistance (No. of repetition) 45.

Oil resistance (scratched with fingeni ails after Good being dipped in transformer oil at room temp. for 24 hrs.)

Table 2 Test itcin 'llicinvontion, Conventional Example 8 insulated \vire None None.

Good. Good.

. do Do.

ii'ountl t Wonnd to 3 twice dim, tinns di:1., Good. Good.

Good Good Seven lengths each of the self bonding magnet wires 1, sisting of polyester, polyurethane, acrylic, epoxy, and

of the invention, of Examples 1, 2, 3 and 8, were assembled in such a manner that a 1.5 cm. portion of one of them was surrounded by the other six lengths, and all of them were tightly bound together. After they were dipped in trichloroethylene for 2 minutes, taken out of it, and heated for 1 hour at 120 C., self-bonding strength test was made with a load attached to the free end of the center length at C., 70 C., 100 C. and 130 C. A similar test was made for the sake of comparison of seven conventional self-bonding magnet wires (on the outside of the polyester resin insulated wire, a varnish consisting mainly of polyvinyl butyral mixed with thermoplastic resin is coated and baked). The results are as per What we claim is:

1. The method of making a self-bonded double coated wire, comprising the steps:

(a) coating the wire with an enamel selected from the group consisting of polyester enamel, polyurethane enamel, acrylic enamel, epoxy enamel, and silicone enamel, and baking said coat, whereby to form a first baked coat;

(b) coating said first coat with mixture of polyvinyl cetal and a resin chosen from the group compatible with polyvinyl acetal consisting of phenol resin, epoxy resin, melamine resin, silicone resin, xylene resin, furane resin, and polyurethane resin, whereby to form a second coat;

(c) underbaking said second coat such that said second coat would swell if dipped for five minutes in a boiling solution comprised initially of toluol and 70% denatured alcohol, by volume:

(d) dipping said wire thus double coated into a solvent of chlorinated aliphatic hydrocarbons to cause said second coat to swell and winding said wire into a coil of contiguous adjacent turns, and

(e) heating said coil at a temperature sufhcient to cause said swelled second coat to adhere together the ad jacent turns.

2. The method of claim 1 wherein said underbaking step includes heating said second coat at a temperature of from 200 to 400 C. for a period of time from 4 to 120 seconda 3. The method of claim 2 wherein step (e) occurs at a temperature of from 100 to 150 C.

4. The method of. making a self-bonding wire, said \virc having a base coating selected from the group consilicone enamels, comprising the steps:

(a) coating said base coat with a mixture of polyvinyl acetal and a resin chosen from the group compatible with said polyvinyl acetal consisting of phenol resin, epoxy resin, melamine resin, silicone resin, xylene resin, furane resin, and polyurethane resin, whereby to form a second coat;

(b) underbaking said second coat such that said second coat would swell if dipped for five minutes in a boiling solution comprised initially of 30% toluol and denatured alcohol, by volume; and

(c) dipping said wire into a solvent of chlorinated aliphatic hydrocarbons to cause said second coat to swell.

5. The method of claim 4, including the additional steps:

(d) winding said wire into a coil of contiguous adjacent turns, after step (b); and

(e) heating said coil at a temperature suflicient to cause id sw ll d se nd coat to adhere together the adjacent turns after steps (c) and (d).

6. The method of making a wire having an insulating coating resistant to chlorinated aliphatic hydrocarbon solvents self-bonding, comprising the steps:

(a) administering to said wire an outer coat with a mixture of polyvinyl acetal and a resin chosen from the group compatible with said polyvinyl acetal consisting of phenol resin, epoxy resin, melamine resin, silicone resin, xylene resin, furane resin, and polyurethane resin;

(h) under-baking said outer coat such that said outer coat would swell if dipped for five minutes in a boiling sollution comprised initially of 30% toluol and 70% denatured alcohol, by volume; and

(c) dipping said wire into a solvent of chlorinated aliphatic hydrocarbons to cause said outer coat to swell.

7. The method of claim 6, wherein said polyvinyl acetal is in the amount of parts by weight and said group compatible therewith is in the amount of 10 to 100 parts by weight, and preferably 20 to 60 parts by weight, and said underbaking occurs in a furnace from 2 to 10 meters long, at a temperature of from 200 to 400 C., and said wire moves at rate of from 5 to 30 meters per minute through said furnace.

8. The method of claim 6, including the additional steps:

(d) winding said wire into a coil of contiguous adjacent turns, after step (b);

(e) heating said coil at a temperature suflicient to cause said swelled outer coat to adhere together the adjacent turns after steps (c) and (d).

9. The method of claim 8, wherein said polyvinyl acetal is in the amount of 100 parts by Weight and said group compatible therewith is in the amount of 10 to 100 parts by weight, preferably 20 to 60 parts by weight, and said underbaking occurs in a furnace from 2 to 10 meters long, at a temperature of from 200 to 400 C., and said wire moves at rate of from 5 to 30 meters per minute through said furnace.

10. The method of making a self-bonded Wire coil, Said Wire having an insulating coat selected from the group consisting of polyester, polyurethane, acrylic, ep-

oxy, and silicone enamels, comprising the steps:

(a) forming an outer coat on said insulating coat with a mixture of 100 parts by weight polyvinyl acetal and 10 to 100 parts by Weight a thermosetting resin chosen from the group consisting of phenol resin, epoxy resin, melamine resin, silicone resin, Xylene resin, furane resin, and polyurethane resin;

(13) underbaking said outer coat at a temperature from 200 to 400 C. for a period of time from 4 to 120 seconds;

(c) dipping said outer coat into a chlorinated aliphatic hydrocarbon solvent having one to four carbon atoms for a time sufiicient to cause said outer coat to swell and winding said Wire into a coil of contiguous adjacent turns;

(d) heating said coil at a temperature of from 100 to 150 C. for a time sufficient to vaporize the solvent.

References Cited by the Examiner UNITED STATES PATENTS 2,523,037 9/1950 Mathes 117-l2l 2,916,403 12/1959 'Calderwood 1 17218 3,038,831 6/1962 Rosenberg l56173 3,059,046 10/1962 Westervelt et al s 1741 10 3,104,236 9/1963 Lavin et a1. ]17-232 3,239,598 3/1966 Olson et a1 ll7-218 FOREIGN PATENTS 950,383 2/1964 Great Britain.

ALFRED L. LEAVITT, Primary Examiner.

RICHARD D. NEVIUS, Examiner.

W. L. JARVIS, Assistant Examiner. 

1. THE METHOD OF MAKING A SELF-BONDED DOUBLE COATED WIRE, COMPRISING THE STEPS: (A) COATING THE WIRE WITH AN ENAMEL SELECTED FROM THE GROUP CONSISTING OF POLYESTER ENAMEL, POLYURETHANE ENAMEL, ACRYLIC ENAMEL, EPOXY ENAMEL, AND SILICONE ENAMEL, AND BAKING SAID COAT, WHEREBY TO FORM A FIRST BAKED COAT; (B) COATING SAID FIRST COAT WITH A MIXTURE OF POLYVINYL ACETAL AND A RESIN CHOSEN FROM THE GROUP COMPATIBLE WITH SAID POLYVINYL ACETAL CONSISTING OF PHENOL RESIN, EPOXY RESIN, MELAMINE RESIN, SILICONE RESIN, XYLENE RESIN, FURANE RESIN, AND POLYURETHANE RESIN, WHEREBY TO FORM A SECOND COAT; (C) UNDERBAKING SAID SECOND COAT SUCH THAT SAID SECOND COAT WOULD SWELL IF DIPPED FOR FIVE MINUTES IN A BOILING SOLUTION COMPRISED INITIALLY OF 30% TOLUOL AND 70% DENATURED ALCOHOL, BY VOLUME; (D) DIPPING SAID WIRE THUS DOUBLE COATED INTO A SOLVENT OF CHLORINATED ALIPHATIC HYDROCARBONS TO CAUSE SAID SECOND COAT TO SWELL AND WINDING SAID WIRE INTO A COIL OF CONTIGUOUS ADJACENT TURNS, AND (E) HEATING SAID COIL AT A TEMPERATURE SUFFICIENT TO CAUSE SAID SWELLED SECOND COAT TO ADHERE TOGETHER THE ADJACENT TURNS. 